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DNA corresponding to 16S rDNA and the 16S-23S rDNA intergenic spacer (ITS) from 22 reference strains of acetic acid bacteria, representing the diversity of the family Acetobacteraceae, and 24 indigenous acetic acid bacteria isolated from wine fermentations were analysed by PCR-RFLP. Frateuria aurantia LMG 1558 T and Escherichia coli ATCC 11775 T were included as outgroups. PCRamplified products of about 1450 bp were obtained from the 16S rDNA of all the strains and products of between 675 and 800 bp were obtained from the 16S-23S rDNA ITS. PCR products were digested with 4-base-cutting restriction enzymes in order to evaluate the degree of polymorphism existing among these strains. Of the enzymes tested, TaqI and RsaI were the most discriminatory and showed no intraspecific variations in the restriction patterns. Restriction analysis of the 16S rDNA with these enzymes is proposed as a rapid and reliable method to identify acetic acid bacteria at the level of genus and species (or related species group) and its applicability to identification of indigenous acetic acid bacteria was demonstrated. The same degree of distinction as that for the 16S rDNA analysis was obtained within reference strains of acetic acid bacteria by PCR-RFLP of the 16S-23S rDNA ITS. However, 16S-23S rDNA ITS restriction patterns of strains isolated from wine did not match those of any of the reference strains. Thus, PCR-RFLP of the 16S-23S rDNA ITS is not a useful method to identify isolates of acetic acid bacteria at the species level, although it may be an adequate method to detect intraspecific differentiation.

Yeast ecology, biogeography and biodiversity are important and interesting topics of research. The population dynamics of yeasts in several cellars of two Spanish wine-producing regions was analysed for three consecutive years (1996 to 1998). No yeast starter cultures had been used in these wineries which therefore provided an ideal winemaking environment to investigate the dynamics of grape-related indigenous yeast populations. Non-Saccharomyces yeast species were identified by RFLPs of their rDNA, while Saccharomyces species and strains were identified by RFLPs of their mtDNA. This study confirmed the findings of other reports that non-Saccharomyces species were limited to the early stages of fermentation whilst Saccharomyces dominated towards the end of the alcoholic fermentation. However, significant differences were found with previous studies, such as the survival of non-Saccharomyces species in stages with high alcohol content and a large variability of Saccharomyces strains (a total of 112, all of them identified as Saccharomyces cerevisiae) with no clear predominance of any strain throughout all the fermentation, probably related to the absence of killer phenotype and lack of previous inoculation with commercial strains.

Octanoic (C8) and decanoic (C10) acids are produced in hypoxic conditions by the yeast Saccharomyces cerevisiae as by-products of its metabolism and are considered fermentation inhibitors in the presence of ethanol at acidic pH. This study aims to broaden our understanding of the physiological limits between toxicity and ester production in yeast cells. To this end, the non-inhibitory concentration (NIC) and maximum inhibitory concentration (MIC) values were first established for C8 and C10 at physiological pH (5.8) without ethanol. The results showed that when these acids were added to culture medium at these values, they tended to accumulate in different cellular fractions of the yeast. While C8 was almost entirely located in the cell wall fraction, C10 was found in the endocellular fraction. Cell fatty acid detoxification was also different; while the esterification of fatty acids was more efficient in the case of C10, the peroxisome was activated regardless of which fatty acid was added. Furthermore, the study of the Pdr12 and Tpo1 transporters that evolved during the detoxification process revealed that C8 was mostly expelled by the Pdr12 carrier, which was related to higher β-oxidative damage in the presence of endocellular C10. C10 is more toxic at lower concentrations than C8. Although they are produced by yeast, the resulting intracellular medium-chain fatty acids (MCFAs) caused a level of toxicity which promoted cell death. However, MCFAs are involved in the production of beverage flavours.

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